Influence of the Processes Parameters on the Properties of The ...

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
Figure 5.7: Desorption <strong>of</strong> CO 2 from PLGA 50:50 after 100 and
200 bars, at T sat = 36.5°C and t sat = 120 min.
Table 5.7 shows that <strong>the</strong> desorption-diffusion coefficient <strong>of</strong> CO 2 is increasing, in <strong>the</strong> range
between 10 -11 and 10 -9 , with <strong>the</strong> increase <strong>of</strong> <strong>the</strong> saturation time. The desorption-diffusion coefficient, D dp , has
an increasing trend and finally reaches a plateau after 60 minutes for P sat = 125 bar and T sat = 36.5°C with a
value <strong>of</strong> 2.10 -9 m 2 /s. These data proves <strong>the</strong> change in <strong>the</strong> diffusion coefficient with <strong>the</strong> variation <strong>of</strong> CO 2
sorption inside <strong>the</strong> polymer matrix. We can observe from Table 5.7 that <strong>the</strong> sorption <strong>of</strong> CO 2 into <strong>the</strong> polymer
increases with increasing time until it reaches a plateau after 60 minutes. One can say that <strong>the</strong> capacity <strong>of</strong>
sorption increases with <strong>the</strong> sorption <strong>of</strong> CO 2 into <strong>the</strong> polymer.
Table 5.7: Desorption-diffusion coefficients and sorption <strong>of</strong> CO 2 after different saturation times at saturation
pressure 125 bars and saturation temperature 36.5°C.
t sat (min) D dp (m 2 Sorption <strong>of</strong> CO
/ s)
2 into <strong>the</strong> PLGA 50:50
(g CO 2 / g Polymer)
10 7.29 x 10 -11 0.153
20 1.62 x 10 -10 0.195
60 2.01 x 10 -9 0.270
120 2.05 x 10 -9 0.281
240 2.06 x 10 -9 0.281
Also, as shown in Table 5.8, <strong>the</strong> desorption-diffusion coefficient increases with increasing
saturation pressure. Since <strong>the</strong> density <strong>of</strong> CO 2 increases with <strong>the</strong> pressure, it is expected that <strong>the</strong> sorption
capacity increases with <strong>the</strong> increasing pressure. On <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> desorption-diffusion coefficients
calculated for rubbery states, D dp , are always greater than <strong>the</strong> diffusion coefficients after vitrification, D dg .
Table 5.8: Desorption-diffusion coefficients <strong>of</strong> CO 2 from PLGA 50:50 for plasticized and glassy states, after
different saturation pressures at 36.5°C for 120 min <strong>of</strong> saturation time.
P sat (bar) D dp (m 2 / s) D dg (m 2 / s)
55 1.437 x 10 -10 -
80 1.734 x 10 -10 -
100 2.140 x 10 -9 2.321 x 10 -11
125 2.050 x 10 -9 7.727 x 10 -11
150 2.606 x 10 -9 1.753 x 10 -10
200 3.321 x 10 -9 2.854 x 10 -10
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